The invention relates to weld cladding of metallic workpieces and in particular to the cladding of the workpiece having a surface inclined in a direction transverse to the direction of weld travel.
It is known to plate or clad various metallic workpieces by depositing weld metal by submerged arc electric welding. Multiple rod or strip electrodes are used for the purpose of achieving a reasonable width of surface coverage on a single pass. A typical application of such a cladding method would be to clad the interior surface of a cylindrical pressure vessel with a corrosion resistant alloy such as stainless steel. On occasion there is a sloped internal surface where the thickness of the wall plate changes, for instance where the straight portion of the pressure vessel ends and a hemispherical head begins. Such an inclined surface would be at approximately 10.degree. with the axis of the vessel and run for a length of six to eight inches.
While the vessel may be placed in a horizontal position and rotated on rolls for the purpose of strip cladding, the massive size of many vessels makes it difficult to change the orientation of the axis so that the inclined surface can be placed in a horizontal position. Accordingly, there is a need for clad welding an inclined surface.
It is required that the inside surface after cladding be smooth for purposes of ultrasonically testing the structure. This requires grinding in many cases, and any uneven weld deposit increases not only the cost of the material being deposited but the cost of removal of the excess. In prior art methods there were considerable problems with the weld metal running down the slope. Accordingly, each weld bead laid down was limited in width and, in fact, has a substantial overlap of the previously deposited bead. This required substantial grinding of all of the overlap material.
Furthermore, the overlap portion would have a different composition than the portion which was deposited on the base metal. The dilution of the weld deposit by the base metal would occur only where it was deposited directly on the base metal with such dilution being absent in the overlap portion.
Since the molten metal has a high resistance to electric current flow, there tended to be a burn through to the base metal in the shallow end of the weld metal with resultant undercutting of the base metal. Irregular beads formed which could not be controlled.